Giant electrocaloric response in smectic liquid crystals with direct smectic-isotropic transition

Eva Klemenčič,Maja Trček,Zdravko Kutnjak,Samo Kralj

doi:10.1038/s41598-019-38604-9

Eva Klemenčič, Maja Trček + Show 2 more

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https://doi.org/10.1038/s41598-019-38604-9

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Abstract

Electrocaloric materials have become a viable technology for solid state heat management applications. We demonstrate both theoretically and experimentally that liquid crystals (LCs) can be exploited as efficient electrocaloric materials. Numerical and experimental investigations determine the conditions under which the strongest electrocaloric effect (ECE) responses are expected in LCs. Specifically, we show that a large ECE can be expected at the isotropic-nematic and in particular at the isotropic-smectic A phase transition. In our theoretical study, LC ordering is modelled using a Landau – de Gennes - Ginzburg mesoscopic approach. The simulation results are in qualitative agreement with our high precision electrocaloric measurements conducted on 8CB and 12CB liquid crystals. In the latter, we obtained ΔTEC ~ 6.5 K, corresponding to the largest response measured so far in LCs. The fluid property of LC electrocaloric heat cooling elements could lead to the development of devices with a higher coefficient of performance and thus better cooling power yield per mass of the ECE-based device.

Highlights

The electrocaloric effect[1,2] is related to a reversible change in the temperature ΔTEC of a material upon switching an electric field on or off under adiabatic conditions
In expressing FLC, we use the Landau-de Gennes-Ginzburg approach in terms of the nematic tensor order parameter Q and the smectic complex order parameter ψ = ηeiφ
We focus on discontinuous order-disorder Isotropic-Nematic (I-N) or Isotropic-smectic A (SmA) (I-SmA)) phase transitions which display relatively large changes in orientational order entropy contribution

Summary

Introduction

The electrocaloric effect[1,2] is related to a reversible change in the temperature ΔTEC of a material upon switching an electric field on or off under adiabatic conditions. In order to develop commercially competitive ECE-based applications one needs to find adequate electrocaloric (EC) materials that experience sufficient electrocaloric temperature responses, of the order of ΔTEC ∼ 10 K, for moderate changes in an external electric field E. Note that this difference could be further enhanced by an order of magnitude by using active regenerator approaches[19]. One needs EC material exhibiting a relatively large change in entropy on varying E This could be realized near a symmetry breaking order-disorder phase transition in which an order parameter field spontaneously appears in the lower symmetry phase. The sequence of phases depends on the length of aliphatic chains of anisotropic nCB molecules

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